Here is the basic equipment you need to kiteboard:

Kite:  If you will be kiteboarding on the water you will want a Leading Edge Inflatable (LEI) kite that allows for easy water relaunch and flotation in case of emergency.  The lastest generation of kites are much easier to learn on with wider wind ranges and easier water relauch.   These kites range from $800 to $1800 complete depending on size and manufacturer.

Harness:  Your harness transfers the pull of your kite directly to your central torso and also allows the kite to depower.  Waist, seat, and impact are different harness styles that are chosen based on individual kiteboarder preference. 

Board:  Several different board styles are used by kiteboarders.  The most common is a twin-tip board in the 135cm to 155cm range with sandal/footstrap style bindings.  Other styles include directional surf boards, wake shapes with boots, and wide, flat light wind boards.  Boards complete with fins, pads, and straps or bindings range from $400 to $700.

Wetsuit:  Unless you live in the tropics you'll need a neoprene wetsuit to spend hours and hours comfortably in the water.  Most kiteboarders use a 2mm shorty suit for moderate conditions and a 4 mm full suit for spring and fall.  Shorties are avaiable for $60=$80 and full suits $149- $299 depending on thickness and features.

Booties:  When you are learning the sport you will spend alot of time walking through the water with your kite.  To avoid cuts on your feet from random sticks, zebra muscles, shrapnel, shells, ect... booties/water shoes/aqua socks are recomended.